IMHO if you can be bothered to send the bits or deliver them, you'll get a very good service from T&L Engineering in Bedfordshire. Proper engine reconditioners. Had cranks ground, barrels bored, barrels resleeved, rods rectified, head work, etc etc - very fair prices and very good work. Google takes you to Thailand and other places, but here's a good link (I think!)
http://www.vintage-engine.net/ There'll be folk further north I'm sure just as good, but if no-one comes up with . . .